A (partial) list of the 450 SL's repairs and upgrades:

Engine compartment:

Repaired broken advance mechanism in distributor.
Lubricated shrieking heater blower motor.
Replaced damaged valve stem seals on #2 hole.
New cam oiler plastic bits.
New rear main seal.
New motor mounts.
New thermostat.
'Upgraded' EGR valve.
New (used) alternator.
Removed belt from noisy air (smog) pump.
New timing chain, guides, and tensioner. I found this in the oil drain pan, and this car was the most likely suspect.
Upgraded windshield washer nozzles with (used) heated ones.
Recharged A/C with R12, and again later with R12-compatible.
Replaced missing cruise control actuator cable.
Replaced missing brake vacuum check valve with good used.
Acid-flushed cooling system.
Replaced missing manifold heat shields.
'Upgraded' smog pump system.
New idle air hoses.
Adjusted (with hammer!) thermostatic idle air valve.

Body:

Welded in new spare tire floor, old one was rusted away.
Welded in new metal at rusted-out front subframe mount.
Welded up cracks in exhaust system: pipes, resonator, and muffler.
New (used) transmission (old one had stripped stator splines). Installed new front and pump seals.
New transmission mount.
New pinion seal on differential.
New driveline flex discs.
New driveline center bearing and support.
Removed heavy rust under battery box. Treated and painted remaining metal.
New (correct) battery.
Made trunk floor carpet out of a floor mat.
Procured used tire and wheel for (missing) spare.
New rubber fuel lines at fuel tank and vapor tank.
New fuel filler neck seal.
New grommets at front hardtop mounts.
New front sway arm bushing kit.
New idler arm bushing kit.
Tightened steering box.
Patched holes in soft top with canvas and fabric glue.
New soft top cover (horse collar) seal.
Glued rattling rear quarter windows in hardtop.
New rear subframe mounts.
Replaced power (manual) antenna with automatic antenna from '83 380 SL. Required new dash switch and wiring, and CLA of new antenna assembly.
New driver door vacuum switch (central locking).
Treated and painted various small 'skin cancers'.
Separated fog light circuit from headlights. Added rear fog light.
Upgraded head and fog lights.
Installed flip-up rear wind screen. (Wonderful!)
Balanced driveline, due to boo-boo during transmission work.
New driveline centering bushings.
New differential mount.
Cleaned and lubed trunk light switch.

Cabin:

New sunvisors. (Old ones resembled sawdust-filled socks with coathangers stuck inside.)
Cut open loose steering wheel foam and reglued with RTV.
Added leather 'wheelskin' wrap to steering wheel.
New emblem in steering wheel.
Added outside temperature display from a 190E.
Added headlight-on warning circuit (using a small relay).
Replaced defective capacitor in cruise control amplifier. Resoldered.
Lubed shrieking speedometer. (Twice, now.)
Cleaned instrument cluster. Repainted sun-faded needles. Replaced cracked 'glass'.
Cleaned and lubed seat tracks.
Welded springs back in place in driver's seat bottom.
Adjusted A/C switch so that heater fan doesn't run all the time.
Replaced blown right speaker with used factory speaker.
Replaced Becker with Alpine CD.
Added speakers to the non-factory rear 'deck'. (Holes were already there.)
Added rear center seat belt to tether a baby seat.
Glued together broken brake release knob.
New vent knobs.
New seat hinge covers.
Metal reinforcement panel glued into driver's seatback cover.
Replaced torn driver's seat bottom cover with a good cover (and pad) from a 190E. Fits good enough!
Repaired right-side heat control (of coolant flow) vacuum switch.
Cracked dash has been filled/painted (Leatherique).
Interior has been painted (Leatherique).
Dome light system from later 560 SL. (PDF)

Still broken:

Rust blisters at rear of trunk lid.
Minor body dents and some sill rust.
Really could use a repaint due to the many surface flaws, though it still looks pretty sharp from a few feet away.
Rear window defroster nearly useless. (Bad glass.)
Left window glass is scratched.